HBr forms azeotrope with water. The strength of constant boiling aqueous HBr solution can be maximum up to about 48%. Constant boiling HBr is very useful as a reagent as well as a reactant for synthesis of various chemical intermediates and chemicals, including pharmaceuticals.
High levels of impurities such as sulfate impurities are not acceptable for commercially important applications of HBr and hence purity of the product obtained is an important criteria which the manufacturing process must fulfill.
Conventionally, to obtain aqueous hydrobromic acid of desired strength and purity, double distillation and/or precipitation is carried out for removal of sulfate impurities. Double distillation and/or precipitation adds to and extra step and cost of the process. It also consumes extra energy and increases environmental load.
Hydrobromic acid can be prepared by reaction of bromine with sulfur and water in accordance with the following reaction:3Br2+S+4H2O→H2SO4+6HBr
However, this reaction is slow and the reaction mixture requires to be vigorously stirred. The reaction mass remains cold initially and then there is a sudden rise in temperature causing bromine to evaporate. To overcome this problem, Frieda et al. have developed a process (U.S. Pat. No. 2,342,465) which comprises of two steps: in the first step, sulfur is dissolved in bromine so as to obtain sulfur bromide as follows:Br2+2S→S2Br2 
S2Br2 thus formed is then reacted further with bromine and water to produce HBr and H2SO4 as follows:S2Br2+5Br2+8H2O→2H2SO4+12HBr
Hydrobromic acid is recovered by distillation to obtain 42% HBr. Or alternatively sulfuric acid is removed by precipitation with barium carbonate.
CN1126174 discloses a process for preparing hydrobromic acid, said process includes reaction of bromine, sulfur and water at 20-50 deg.C for 1.5-20 hrs, filtering, distillation at 80-110 deg.C and addition of barium hydroxide to remove sulfuric radicals. A method for continuous preparation of hydrobromic acid from bromine and sulfur is reported by Mandalia et al., Indian J. Technol., 1973, 11(9), 406.
USSR 472895 also discloses a method of preparation of HBr from Br2, sulfur and water using MnO2 and V2O5 as catalysts.
In above mentioned methods for preparing HBr from bromine and sulfur, sulfate impurities are present which needs to be removed either by double distillation or by precipitation which adds to energy consumption and cost as mentioned above.
Preparation of hydrobromic acid from bromine, carbon and water is also reported in the literature (U.S. Pat. No. 1,870,308). In this process, carbon is oxidized to carbon dioxide and bromine is converted into hydrogen bromide which dissolves in excess water. This process requires reactants in high purity because if carbon contains HBr soluble matter, the impurities need to be removed by treatment of carbon before the reaction.
U.S. Pat. No. 1,379,731 discloses a method of manufacturing HBr by direct distillation from a reaction mixture comprising alkali bromide (such as sodium bromide) and mineral acid (sulfuric acid).
A process for conversion of sodium bromide to hydrobromic acid and sodium bisulfate has been reported in the patent application US2004/0067191.
A continuous process for making hydrobromic acid from bromine and hydrogen and dissolution thereof in water to obtain HBr is disclosed in U.S. Pat. No. 1,398,596. GB154472, U.S. Pat. Nos. 1,905,432, 1,380,084 and 2,070,263 also discloses a method for manufacturing hydrobromic acid from bromine and hydrogen. These methods require isolation of bromine and reaction with hydrogen which is hazardous.
RO111839 discloses a method of manufacturing HBr from sodium bromide and concentrated sulfuric acid to produce hydrobromic acid which is then sparged into azeotropous hydrobromic acid, until the desired concentration is obtained. Removal of sulfate impurities is a problem in this method also.
Israeli 39120 discloses a method of producing HBr free of Br2 comprising treating brine such as Dead Sea brine in a reactor containing a fluidized bed of particles maintained in fluidized state by upward passage of gases at 800-1300° C.
Separation of aqueous HBr from an aqueous solutions containing mixture of HBr, HCl and H2SO4 has been reported in USSR709522. The method comprises fractional distillation followed by condensation of the acid vapor. The method was improved by distilling and condensing at 0.35-0.5 atm., by concentrating the solution during separation of HCl to an HBr content in the vapor of 44-9%, and by distilling during HBr separation to an H2SO4 concentration in the pot residue of 58-70%.
The abovementioned methods for producing hydrobromic acid reported in the prior art involve energy consuming process. Moreover, sulfate impurities are present in the product which compels one either for double distillation or treatment with precipitating agent such as barium carbonate to get rid of sulfates. Present invention overcomes abovementioned drawbacks of prior art.
Closest prior art JP78149895 (application number JP19770066175) discloses a method for production of hydrogen bromide gas and sulfuric acid from bromine and sulfur dioxide. However, it requires higher temperature and prior-isolation of bromine for carrying out the process. The present invention consumes lesser energy and it also obviates the need for isolation of bromine. In the present invention, bromine is generated in situ from bittern and it is reacted with SO2 without the need for isolation of bromine. Present invention also obviates the need for removal of sulfur by precipitation. The invented process is simple, cost effective and safer compared to the prior art.